In recent years, energy storage devices, especially lithium secondary batteries have been widely used in small-sized electronic devices, such as mobile telephones, notebook-size personal computers and the like, in electric vehicles, and for electric power storage. These electronic devices and vehicles may be used in a broad temperature range at midsummer high temperatures or at frigid low temperatures, and are therefore required to have well-balanced and improved electrochemical characteristics in a broad temperature range.
In particular, for preventing global warming, CO2 emission reduction has now become imperative, and among environment-responsive vehicles equipped with energy storage devices such as lithium secondary batteries, capacitors and the like, early popularization of hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) is desired. Vehicles may take a long travel distance and therefore may be used in the region of a widely-varying temperature range that covers from an extremely hot region of the tropical zone to a frigid region. Consequently, it is required that the electrochemical characteristics of those storage devices to be mounted on such vehicles should not be deteriorated even in use in a broad temperature range varying from high temperatures to low temperatures.
In this specification, the term of lithium secondary batteries is used as the concept that includes also so-called lithium ion secondary batteries.
A lithium secondary battery is mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt and a nonaqueous solvent. For the nonaqueous solvent, used are carbonates, such as ethylene carbonate (EC), propylene carbonate (PC), etc.
As the negative electrode of the lithium secondary battery, known are metal lithium, and metal compounds (metal elemental substances, oxides, alloys with lithium, etc.) and carbon materials capable of absorbing and releasing lithium. In particular, a lithium secondary battery using a carbon material capable of absorbing and releasing lithium, such as coke, artificial graphite, natural graphite or the like, has been widely put into practical use.
For example, it is known that, in a lithium secondary battery that uses a highly-crystallized carbon material, such as natural graphite, artificial graphite or the like, as the negative electrode material therein, the solvent in the nonaqueous electrolytic solution undergoes reductive decomposition on the surface of the negative electrode during charging and the decomposed products and gases generated through the decomposition detract from the desired electrochemical reaction in the battery to thereby worsen the cycle properties of the battery. In addition, when the decomposed products of the nonaqueous solvent accumulate, then lithium could not be smoothly absorbed and released by the negative electrode and the electrochemical characteristics of the battery would be thereby worsened in a broad temperature range.
Further, it is known that a lithium secondary battery using a lithium metal or its alloy, or a metal elemental substance, such as tin, silicon or the like or its metal oxide as the negative electrode material therein may have a high initial battery capacity but the battery capacity and the battery performance thereof, such as cycle properties greatly worsens, since the micronized powdering of the material is promoted during cycles thereby bringing about accelerated reductive decomposition of the nonaqueous solvent, as compared with the negative electrode of a carbon material. In addition, the micronized powdering of the negative electrode material and the accumulation of the decomposed products of the nonaqueous solvent would interfere with smooth absorption and release of lithium by the negative electrode, thereby often worsening the electrochemical characteristics in a broad temperature range of the battery.
On the other hand, it is also known that, in a lithium secondary battery using, for example, LiCoO2, LiMn2O4, LiNiO2, LiFePO4 or the like as the positive electrode, the nonaqueous solvent in the nonaqueous electrolytic solution locally undergoes partial oxidative decomposition in the interface between the positive electrode material and the nonaqueous electrolytic solution in a charged state and the decomposed products and gases generated through the decomposition interfere with the desired electrochemical reaction in the battery, thereby also worsening the electrochemical characteristics in a broad temperature range of the battery.
As in the above, the decomposed products and gases generated through decomposition of the nonaqueous electrolytic solution in the positive electrode and the negative electrode interfere with lithium ion movement and cause battery swelling, and the battery performance is thereby worsened. Despite the situation, electronic appliances equipped with lithium secondary batteries therein are offering more and more an increasing range of functions and are being in a stream of further increase in power consumption. With that, the capacity of lithium secondary batteries is being much increased, and the space volume for the nonaqueous electrolytic solution in the battery is decreased by increasing the density of the electrode and by reducing the useless space volume in the battery. Accordingly, the situation is that even decomposition of only a small amount of nonaqueous electrolytic solution may worsen the electrochemical characteristics in a broad temperature range of the battery.
PTL 1 proposes a nonaqueous electrolytic solution containing 1,5,2,4-dioxadithiepane 2,2,4,4-tetraoxide, and suggests improvement of cycle properties and storage properties.
PTL 2 proposes a nonaqueous electrolytic solution containing diphenylmethane disulfonate, and suggests improvement of cycle properties and storage properties.
PTL 3 proposes a nonaqueous electrolytic solution containing dimethyl malonate, and suggests improvement of overcharge properties.
PTL 4 proposes a nonaqueous electrolytic solution containing 2,4-difluorophenyl acetate, and suggests improvement of overcharge properties and storage properties.